THE UNITED STATES and its European allies want Kosovo to be secure, democratic and multiethnic, but not independent. Redrawing Yugoslavia's boundaries in order to award independence to Kosovo, it is said, could set a problematic precedent elsewhere in the Balkans. If the West has any long-term strategy, then, it is to construct a democratic Kosovo while engineering a democratic Serbia, too, so that someday these two entities can live together and join an economically integrated and politically stabilized Southeastern Europe.

None of this is easy. Democratizing Serbia is especially difficult given Slobodan Milosevic's ruthlessness, his opponents' fecklessness and the indirectness of the means the West is using--that is, economic sanctions. In Kosovo, the allies at least have 50,000 troops on the ground and billions in pledged economic aid to work with. Yet even there, signs of trouble are multiplying--the most dramatic being ethnic violence in the divided town of Mitrovica, where Serbs and Albanians have traded gunfire with one another and with NATO troops.

Serbs, who control the north section of town, fear violent revenge of the kind Albanians have meted out too often, with too tepid a NATO response, since the war's end. Albanians fear that Serbs will launch a pogrom against the few Albanians left in the Serb neighborhood. These fears are stoked and manipulated by forces opposed to a democratic, multiethnic Kosovo: Kosovo Liberation Army extremists who want to capture the mineral resources on the Serbian side of town for the independent state they still envision, and agents of Mr. Milosevic, who wants to create a quagmire from which NATO will be desperate to exit.

All the more important that Mitrovica be treated as a wake-up call. Gen. Henry Shelton, chairman of the Joint Chiefs of Staff, complained yesterday that U.S. and other peacekeepers are just "marking time" in Kosovo. He's right. But the answer is not to pull out or begin shaping exit strategies. Any visible diminution of allied resolve would embolden all of those, Serb and Albanian, seeking to tear the province apart. Instead, the United States, Europe and the alphabet soup of United Nations agencies currently attempting to run Kosovo need to crack down on violence and, as Gen. Shelton suggested, swiftly improve the woefully inadequate civil administration. Europe, especially, must honor the commitments of financial aid and police personnel it already has made.